This invention relates to ultrasonic testing of elongated workpieces such as railroad rails. More particularly, it relates to the testing of unlaid rails as opposed to the testing of rails in track.
A common flaw found in railroad rails, particularly the first rail produced from an ingot, is an open seam within the web of the rail. The flaw, being a longitudinal separation within the web, is often referred to as "pipe." Such flaws cause welding problems which delay production. They also weaken the load supporting web of a rail. Rails having the flaws are rejected for the sake of safety and in order to avoid welding delays and future costs of replacement.
As pipe flaws are generally totally enclosed within the rail web, they cannot generally be detected by mere visual inspection. However, ultrasonic inspection devices have been used. In these devices, an ultrasonic signal is transmitted from a transducer and the reflection of the ultrasonic signal is detected. The detection may be by the ultrasonic transmitting crystal or by another spaced crystal. If the signal is reflected by a flaw before it reaches the back surface of the rail web, the reflection signal received at the receiver will be advanced in time from that ordinarily received from the back surface. A monitor detects the change in the received signal and indicates a flaw in the rail web.
The ultrasonic transducer is generally mounted in a small search unit which has a very limited inspection region because of the necessity to maintain adequate coupling to a concave surface. Accordingly, it must be passed ("scrubbed") up and down the height of the web as well as along the length of the web. Also, the web surface is not parallel with the web center plane across the height of the web which is the major flaw plane. Subsequently, ability to detect a flaw decreases as the angle between the transducer and the flaw plane of the web increases with movement of the transducer toward the rail head or base.